Toxic apportionment: a causation and risk contribution model.

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Toxic apportionment: a causation and risk contribution model.

I. Introduction and Summary

A. The Basic Idea

In a typical toxic tort case,(1) the plaintiff or the plaintiffs property suffers some harm as a result of exposure to one or more sources of a toxic substance.(2) For example, if the plaintiff has been exposed to asbestos-containing materials(3) and has a history of cigarette smoking, and after years of exposure to both develops a cancer of the lungs, the question arises in tort law as to which of the exposures caused the cancer. However, under the current state of medical knowledge, the question of which toxic substance, if either, actually caused the cancer cannot be answered definitively.(4) If the exposed person sues asbestos manufacturers for products liability, he will have to attempt to prove that the exposure to asbestos-containing materials was either the but-for cause(5) of or a substantial causal factor in the cancer.(6) The trial of such a case will no doubt produce conflicting expert testimony, with the plaintiffs experts stressing the well-established causal relationship between certain cancers and asbestos exposure by inhalation,(7) and the defendant's experts stressing with equally well-documented data the causal relationship between smoking and lung cancer.(8) If the duration and extent of the exposures are significant enough that epidemiological data would support a plausible argument that each is a cause of the plaintiffs cancer, then the data do not warrant concluding that only the defendant's product or only the plaintiff's smoking should be regarded as the cause, thereby requiring either the defendant or the plaintiff to bear the entire loss.(9)

One method of avoiding an all-or-nothing outcome in such a case is to apply principles of apportionment: the plaintiffs cancer would be apportioned among the parties on the basis of the comparative cancer risks each created through its conduct. Nevertheless, this risk contribution model would not predicate liability based solely on risk creation, as the plaintiff must sustain actual harm and those risks created also must be "a' cause of that actual harm. Apportionment using a risk contribution model also avoids the rubric of "fault" that results when courts apportion liability under comparative negligence or fault-based schemes,(10) and it yields fairer and more efficient results than those achieved under some of the alternative causation models employed by courts over the last few decades.(11) For example, some courts hold that so long as a plaintiff demonstrates that asbestos exposure is a substantial factor in bringing about the cancer, the defendant is liable for the entire loss, whether or not there may be other causal factors.(12) In our smoking and asbestos exposure example, courts until recently were reluctant to find a reasonable basis on which to predicate an apportionment of the harm, and, as a result, our plaintiff would recover all of his damages despite the obvious relevance of a history of smoking.(13)

If the plaintiffs asbestos exposure and his smoking are both shown to be causal factors in the plaintiffs lung cancer, then the loss is necessarily capable of apportionment on the basis of the relative risks demonstrated for each kind of toxic exposure. From the perspective of individualized justice, the model produces a fairer result than nonapportionment. Because notions of individualized justice place emphasis on individual accountability, if a party's own conduct creates a kind of risk known to result in the harm complained of, then that party should bear a portion of the loss. Moreover, by apportioning the harm among the respective risk contributors, each pays no more than the portion of the harm fairly attributable to it. Thus, so long as individual responsibility is a valued goal of tort law, courts should apportion losses to reflect the contribution of each responsible party based on the risks each created.

Requiring the defendant to bear the entire loss is inefficient because it eliminates an incentive for persons to provide for their own health and safety. At the other extreme, having the plaintiff bear the entire loss is also inefficient because defendants then lack the incentive to avoid creating toxic-related risks. Apportionment of harm should yield the optimal measure of deterrence: if the defendants are liable only for a portion of the total harm, consistent with the risks they created, it will avoid both the underdeterrence and overdeterrence that result from placing the entire loss on either the plaintiffs or defendants. Moreover, the plaintiffs have an incentive to engage in safer lifestyles, an incentive that is missing if the defendants bear the entire loss.

In addition to requiring an analysis of the relative contribution of risk, this model demands proof of causation. In our smoking and asbestos exposure example, each party's proofs must be sufficient to make out a submissible issue on causation - that the toxic exposure was "a" cause of the harm, ...

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